Cellular phone and method of operating the same

ABSTRACT

A cellular phone covering a plurality of frequency bands, includes (a) an antenna, (b) a high-frequency circuit, (c) an antenna-matching circuit electrically connecting in series between the antenna and the high-frequency circuit, and (d) a first unit which varies a ground length in accordance with a frequency band in which the cellular phone makes communication with others, the ground length being defined as a length of a ground area for the antenna-matching circuit.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a cellular phone, and more particularlyto optimization in antenna performance in a cellular phone covering aplurality of different frequency areas.

[0003] 2. Description of the Related Art

[0004] It is known that an antenna irradiation pattern indicatingantenna characteristic of a cellular phone varies in independence on alength of a ground area of an antenna matching circuit whichelectrically connects an antenna and a high-frequency circuit to eachother. Herein, a ground area indicates a ground of a printed substrateor a die-cast body, for instance. If such a ground area does not have anoptimal length, a lot of poles called a null point appear in an antennairradiation pattern. Herein, a null point means a point at which anantenna gain falls down.

[0005] Some cellular phones such as PDC (personal digital cellular) orW-CDMA (Wideband-Code Division Multiple Access) are designed to be ableto cover a plurality of frequency bands. If such cellular phones have tocover two frequency bands quite different from each other, for instance,800 MHz band and 2 GHz band, it would be quite difficult or almostimpossible to accomplish antenna characteristic by which null points arenot generated, through a single ground length.

[0006] If a lot of null points are generated in an antenna irradiationpattern, an antenna gain much fluctuates in dependence on a position ofa cellular phone, and hence, a level of a signal received from a basestation and a level of a signal transmitted to a base station muchfluctuate, resulting in unstable radio-signal transmission condition.

[0007] Japanese Patent Application Publication No. 7-283631 hassuggested an antenna unit including a radio-signal transceiver arrangedin a body, an antenna device extendable from and retractable into theradio-signal transceiver, and a coil which operates as a matchingcircuit when the antenna device is extended, and operates as a helicalantenna when the antenna device is retracted.

[0008] Japanese Patent Application Publication No. 2001-339474 hassuggested a foldable type cellular phone including a main body, and anantenna matching circuit. The main body is comprised of a first body,and a second body designed pivotable relative to the first body. Theantenna matching circuit is designed to have different characteristicsin accordance with a length of the cellular phone in a folded state anda length of the cellular phone in a non-folded state.

SUMMARY OF THE INVENTION

[0009] In view of the above-mentioned problems in the conventionalcellular phones, it is an object of the present invention to provide acellular phone covering a plurality of frequency bands, which is capableof avoiding generation of null points in an antenna irradiation patternfor accomplishing desired antenna performance.

[0010] It is also an object of the present invention to provide a methodof operating a cellular phone covering a plurality of frequency bandswhich method is capable of doing the same.

[0011] In a cellular phone, since an antenna is arranged in a smallbody, a current runs also through the body. As a result, the body actsas a part of an antenna. Hence, impedance characteristic and antennairradiation pattern are varied in comparison with designed ones.

[0012] In addition, a cellular phone originally has a factor causing aloss to an antenna. A cellular phone includes a circuit part which iscomposed of non-metal, in its body. This results in that the circuitpart would cause a loss when an antenna current runs into the body ofthe cellular phone.

[0013] With respect to a hand-held type cellular phone, a user holds abody of the cellular phone with his hand during making communication.Hence, if an antenna current runs through the body, a user's hand causesa loss.

[0014] In view of the above-mentioned matters, a body of a cellularphone has to be taken into consideration when an antenna of a cellularphone is designed. The present invention is based on this discovery.

[0015] In one aspect of the present invention, there is provided acellular phone covering a plurality of frequency bands, including (a) anantenna, (b) a high-frequency circuit, (c) an antenna-matching circuitelectrically connecting in series between the antenna and thehigh-frequency circuit, and (d) a first unit which varies a groundlength in accordance with a frequency band in which the cellular phonemakes communication with others, the ground length being defined as alength of a ground area for the antenna-matching circuit.

[0016] The first unit may be comprised of (d1) a detector which detectsa frequency band in which the cellular phone makes communication withothers, and transmits a detection signal indicative of the thus detectedfrequency band, and (d2) a second unit which receives the detectionsignal, and varies the ground length in accordance with a frequency bandindicated in the detection signal.

[0017] The cellular phone may be designed to further include a firstprinted substrate, in which case, the second unit may be comprised of afirst switch formed on the first printed substrate, wherein the firstswitch is grounded when the detection signal indicates a first frequencyband, and makes an impedance circuit when the detection signal indicatesa second frequency band greater than the first frequency band.

[0018] The second unit may further include a first inductance, in whichcase, the first switch is electrically connected to the first inductanceto thereby make the impedance circuit when the detection signalindicates the second frequency band.

[0019] The first switch may be comprised of an electrically controllableswitch which is automatically grounded or automatically makes theimpedance circuit in accordance with a frequency band indicated in thedetection signal.

[0020] The cellular phone may further include first to N-th printedsubstrates wherein N is a positive integer equal to or greater than two,in which case, the second unit may be comprised of first to N-thswitches formed on the first to N-th printed substrates, respectively,the first to N-th switches operate in synchronization with one another,and the first to N-th switches are grounded when the detection signalindicates a first frequency band, and make an impedance circuit when thedetection signal indicates a second frequency band greater than thefirst frequency band.

[0021] The second unit may further include first to N-th inductances, inwhich case, the first to N-th switches are electrically connected to thefirst to N-th inductances, respectively, to thereby make the impedancecircuit when the detection signal indicates the second frequency band.

[0022] Each of the first to N-th switches may be comprised of anelectrically controllable switch which is automatically grounded orautomatically makes the impedance circuit in accordance with a frequencyband indicated in the detection signal.

[0023] The first to N-th switches may be electrically connected to oneanother through a cable to which the detection signal is transmittedsuch that the first to N-th switches operate in synchronization with oneanother.

[0024] For instance, the cellular phone is of a straight type or a slidetype.

[0025] The cellular phone may be comprised of a first body, and a secondbody mechanically connected to the first body through a hinge such thatthe second body is rotatable at an end thereof relative to the firstbody, in which case, the cellular phone may further include a firstprinted substrate arranged in the first body, and a second printedsubstrate arranged in the second body, the second unit may furtherinclude a first switch formed on the first printed substrate, and asecond switch formed on the second printed substrate and is driven insynchronization with the first switch, and it is preferable that thefirst and second switches are grounded when the detection signalindicates a first frequency band, and make an impedance circuit when thedetection signal indicates a second frequency band greater than thefirst frequency band.

[0026] The second unit may further include first and second inductances,in which case, the first and second switches are electrically connectedto the first and second inductances, respectively, to thereby make theimpedance circuit when the detection signal indicates the secondfrequency band.

[0027] Each of the first and second switches is comprised of anelectrically controllable switch which is automatically grounded orautomatically makes the impedance circuit in accordance with a frequencyband indicated in the detection signal.

[0028] It is preferable that the first and second switches areelectrically connected to each other through a cable to which thedetection signal is transmitted such that the first and second switchesoperate in synchronization with each other.

[0029] The cellular phone may be comprised of a first body, and a secondbody mechanically connected to the first body through a hinge such thatthe second body is rotatable at an end thereof relative to the firstbody, in which case, the first unit may be comprised of (d1) a detectorwhich detects whether the first and second bodies are open or closed toeach other, and transmits a second detection signal indicative of thedetection of the second detector, and (d2) a second unit which receivesthe detection signal, and varies the ground length in accordance withthe detection of the second detector.

[0030] The second unit may further include first and second inductances,in which case, the first and second switches are electrically connectedto the first and second inductances, respectively, to thereby make theimpedance circuit when the detection signal indicates the secondfrequency band.

[0031] Each of the first and second switches may be comprised of anelectrically controllable switch which is automatically grounded orautomatically makes the impedance circuit in accordance with a frequencyband indicated in the detection signal.

[0032] It is preferable that the first and second switches areelectrically connected to each other through a cable to which thedetection signal is transmitted such that the first and second switchesoperate in synchronization with each other.

[0033] In another aspect of the present invention, there is provided amethod of operating a cellular phone covering a plurality of frequencybands, including the steps of (a) detecting a frequency band in whichthe cellular phone makes communication with others, and (b) varying aground length in accordance with the frequency band detected in the step(a), the ground length being defined as a length of a ground area for anantenna-matching circuit of the cellular phone.

[0034] The cellular phone includes a first printed substrate, and afirst switch formed on the first printed substrate, in which case, themethod may further include the step of grounding the first switch whenthe cellular phone makes communication in a first frequency band, andcausing the first switch to make an impedance circuit when the cellularphone makes communication in a second frequency band greater than thefirst frequency band.

[0035] The cellular phone further includes a first inductance, in whichcase, the method may further include the step of electrically connectingthe first switch to the first inductance to thereby make the impedancecircuit.

[0036] The cellular phone further includes first to N-th printedsubstrates wherein N is a positive integer equal to or greater than two,and first to N-th switches formed on the first to N-th printedsubstrates, respectively, and the first to N-th switches operate insynchronization with one another, in which case, the method may furtherinclude the step of grounding the first to N-th switches when thecellular phone makes communication in a first frequency band, andcausing the first to N-th switches to make an impedance circuit when thecellular phone makes communication in a second frequency band greaterthan the first frequency band.

[0037] The cellular phone further includes first to N-th inductances, inwhich case, the method may further include the step of electricallyconnecting the first to N-th switches to the first to N-th inductances,respectively, to thereby make the impedance circuit.

[0038] There is further provided a method of operating a cellular phonecovering a plurality of frequency bands, the cellular phone beingcomprised of a first body, and a second body mechanically connected tothe first body through a hinge such that the second body is rotatable atan end thereof relative to the first body, the method including thesteps of (a) detecting whether the first and second bodies are open orclosed to each other, and (b) varying a ground length in accordance withthe result of the step (a), the ground length being defined as a lengthof a ground area for an antenna-matching circuit of the cellular phone.

[0039] The cellular phone includes a first printed substrate arranged inthe first body, a first switch formed on the first printed substrate, asecond printed substrate arranged in the second body, and a secondswitch formed on the second printed substrate, in which case, the methodmay further include the step of grounding the first and second switcheswhen the cellular phone makes communication in a first frequency band,and causing the first and second switches to make an impedance circuitwhen the cellular phone makes communication in a second frequency bandgreater than the first frequency band.

[0040] The cellular phone further includes first and second inductances,in which case, the method may further include the step of electricallyconnecting the first and second switches to the first and secondinductances, respectively, to thereby make the impedance circuit.

[0041] In still another aspect of the present invention, there isprovided a program for causing a computer to carry out a method ofoperating a cellular phone covering a plurality of frequency bands,processing executed by the computer in accordance with the programincluding (a) detecting a frequency band in which the cellular phonemakes communication with others, and (b) varying a ground length inaccordance with the frequency band detected in the processing (a), theground length being defined as a length of a ground area for anantenna-matching circuit of the cellular phone.

[0042] There is further provided a program for causing a computer tocarry out a method of operating a cellular phone covering a plurality offrequency bands, the cellular phone being comprised of a first body, anda second body mechanically connected to the first body through a hingesuch that the second body is rotatable at an end thereof relative to thefirst body, processing executed by the computer in accordance with theprogram including (a) detecting whether the first and second bodies areopen or closed to each other, and (b) varying a ground length inaccordance with the result of the step (a), the ground length beingdefined as a length of a ground area for an antenna-matching circuit ofthe cellular phone.

[0043] The above and other objects and advantageous features of thepresent invention will be made apparent from the following descriptionmade with reference to the accompanying drawings, in which likereference characters designate the same or similar parts throughout thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]FIG. 1 is a-perspective view of a cellular phone in accordancewith the first embodiment of the present invention.

[0045]FIG. 2 is a block diagram of the cellular phone illustrated inFIG. 1.

[0046]FIG. 3 is a flow chart showing respective steps to be carried outin an operation of the cellular phone illustrated in FIG. 1.

[0047]FIGS. 4 and 5 are perspective views of a cellular phone inaccordance with the second embodiment of the present invention.

[0048]FIG. 6 is a block diagram of the cellular phone illustrated inFIGS. 4 and 5.

[0049]FIG. 7 is a flow chart showing respective steps to be carried outin an operation of the cellular phone illustrated in FIGS. 4 and 5.

[0050]FIGS. 8A and 8B are perspective views of a cellular phone inaccordance with the third embodiment of the present invention.

[0051]FIGS. 9A and 9B illustrate the results of antenna irradiationpattern simulation having been carried out in a certain condition.

[0052]FIGS. 10A and 10B illustrate the results of antenna irradiationpattern simulation having been carried out in another certain condition.

[0053]FIGS. 11A and 11B illustrate the results of antenna irradiationpattern simulation having been carried out in another certain condition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Preferred embodiments in accordance with the present inventionwill be explained hereinbelow with reference to drawings.

[0055] [First Embodiment]

[0056]FIG. 1 is a perspective view of a cellular phone 10 in accordancewith the first embodiment of the present invention.

[0057] The cellular phone 10 in accordance with the present invention isof a straight type.

[0058] The cellular phone 10 has a cubic body 10A. On an upper surface10 a of the cubic body 10A are arranged a plurality of keys 11 throughwhich a user can input data such as figures or letters into the cellularphone 10, and a display screen 12 in which data a user input or receivedmessages are displayed. On a side surface 10 b of the cubic body 10A ismounted an antenna 13.

[0059]FIG. 2 is a block diagram of the cellular phone 10.

[0060] The cellular phone 10 further includes a printed substrate 17arranged in the body 10A of the cellular phone 10, an antenna matchingcircuit 14, a high-frequency circuit 15, a high-frequency switch 16, aninductance coil 18, a frequency-band selecting circuit 19, and a controlcircuit 20.

[0061] The antenna matching circuit 14, the high-frequency circuit 15,the high-frequency switch 16 and the inductance coil 18 are all formedon the printed substrate 17.

[0062] The antenna matching circuit 14 electrically connects the antenna13 and the high-frequency circuit 15 to each other. A radio signalproduced in the high-frequency circuit 15 is transmitted to the antenna13 through the antenna matching circuit 14, and then, irradiated fromthe antenna 13. A radio signal received at the antenna 13 is transmittedto the high-frequency circuit 15 through the antenna matching circuit14. The antenna matching circuit 14 is electrically connected at aground area thereof to a ground area of the printed substrate 17, andsimilarly, the high-frequency circuit 15 is also electrically connectedat a grounded area thereof to a ground area of the printed substrate 17.

[0063] In the cellular phone 10 in accordance with the first embodiment,a ground surface of the printed substrate 17 is used as an antennaground.

[0064] The high-frequency switch 16 includes a base contact 61, acontact plate 61 a designed pivotable around the base contact 61, afirst contact 62 and a second contact 63. The base contact 61 iselectrically connected to the frequency-band selecting circuit 19through the control circuit 20. The first contact 62 is electricallyconnected to a ground area of the printed substrate 17. The secondcontact 63 is electrically connected to the inductance coil 18 which iselectrically connected at one end to a ground area of the printedsubstrate 17.

[0065] The inductance coil 18 has such an inductance that it provides asufficiently high impedance in a high-frequency band.

[0066] The frequency-band selecting circuit 19 selects a frequency bandin accordance with a particular key actuated by a user among the keys11. As an alternative, the frequency-band selecting circuit 19 may bedesigned to detect a frequency band in which the cellular phone 10 makescommunication with others. The frequency-band selecting circuit 19transmits a signal indicative of a frequency band selected by itself, tothe control circuit 20.

[0067] On receipt of the signal from the frequency-band selectingcircuit 19, the control circuit 20 transmits a control signal to thehigh-frequency switch 16. In accordance with the control signal, thecontact plate 61 a makes pivotal movement around the base contact 61 tothereby make electrical contact with the first contact 62 or the secondcontact 63. The pivotal movement of the contact plate 61 a around thebase contact 61 between the first and second contacts 62 and 63 causes aground length in the cellular phone 10 to vary in accordance with afrequency band.

[0068]FIG. 3 is a flow chart showing respective steps to be carried outin an operation of the cellular phone 10 in accordance with the firstembodiment. Hereinbelow is explained an operation of the cellular phone10 with reference to FIG. 3.

[0069] First, the frequency-band selecting circuit 19 selects afrequency band either in accordance with data input by a user into thecellular phone 10 through a particular key among the keys 11 or bydetecting a frequency band in which the cellular phone 10 is makingcommunication, in step S101.

[0070] Then, the frequency-band selecting circuit 19 transmits a signalindicative of the selected frequency band, to the control circuit 20, instep S102.

[0071] On receipt of the signal from the frequency-band selectingcircuit 19, the control circuit 20 transmits a control signal to thehigh-frequency switch 16, in step S103. The control signal includesindication determined by the control circuit 20 in accordance with thesignal transmitted from the frequency-band selecting circuit 19.

[0072] Herein, it is assumed that the cellular phone 10 has to cover twofrequency bands, 800 MHz band and 2 GHz band.

[0073] When the frequency-band selecting circuit 19 selects 800 MHz (YESin step S104), the contact plate 61 a is caused to make pivotal movementin a counter clock-wise direction to make electrical contact with thefirst contact 62, in step S105. Thus, the body 10A of the cellular phone10 is electrically connected directly to a ground area of the printedsubstrate 17. As a result, the cellular phone 10 would have a firstground length.

[0074] When the frequency-band selecting circuit 19 selects 2 GHz (No instep S104), the contact plate 61 a is caused to make pivotal movement ina clock-wise direction to make electrical contact with the secondcontact 63, in step S106. Thus, the body 10A of the cellular phone 10 iselectrically connected to a ground area of the printed substrate 17through the inductance coil 18. As a result, the cellular phone 10 wouldhave a second ground length smaller than the first ground length.

[0075] Thus, it is possible in the cellular phone 10 to switch a lengthof a ground area with respect to the antenna matching circuit 14.

[0076] [Second Embodiment]

[0077]FIGS. 4 and 5 are perspective views of a cellular phone 30 inaccordance with the second embodiment of the present invention.

[0078] As best illustrated in FIG. 4, the cellular phone 30 is designedto include a first body 31 and a second body 32. The first body 31 ismechanically connected at one end thereof to the second body 32 througha hinge 33 such that the first and second bodies 31 and 32 are rotatableabout the hinge 33 to each other. Specifically, the first and secondbodies 31 and 32 can have a first position in which they are open toeach other as illustrated in FIG. 4, and a second position in which theyare closed to each other as illustrated in FIG. 5.

[0079] A plurality of keys 34 are arranged on a surface 321 of thesecond body 32 which surface 321 is located internal when the first andsecond bodies 31 and 32 are closed to each other. A user can input datainto the cellular phone 30 through the keys 14.

[0080] A liquid crystal display 15 is arranged at the center of asurface 311 of the first body 31 located internal when the first andsecond bodies 31 and 32 are closed to each other. On the liquid crystaldisplay 15 are displayed data which a user input through the keys 14, acontent of an e-mail having been received, or a telephone number of aperson who made a call to the cellular phone 30.

[0081] An extendable antenna 36 is mounted on a rear surface of thefirst body 31.

[0082]FIG. 6 is a block diagram of the cellular phone 30.

[0083] The cellular phone 30 further includes a first printed substrate37 a arranged in the first body 31, a second printed substrate 37 barranged in the second body 32, an antenna matching circuit 38, ahigh-frequency circuit 39, a first high-frequency switch 40, a secondhigh-frequency switch 41, a first inductance coil 42, a secondinductance coil 43, a detecting circuit 44, a frequency-band selectingcircuit 45, and a control circuit 46.

[0084] The antenna matching circuit 38, the high-frequency circuit 39,the first high-frequency switch 40 and the first inductance coil 42 areall formed on the first printed substrate 37 a. The secondhigh-frequency switch 41 is formed on the second printed substrate 37 b.

[0085] The antenna matching circuit 38 electrically connects the antenna36 and the high-frequency circuit 39 to each other. A radio signalproduced in the high-frequency circuit 39 is transmitted to the antenna36 through the antenna matching circuit 38, and then, irradiated fromthe antenna 36. A radio signal received at the antenna 36 is transmittedto the high-frequency circuit 39 through the antenna matching circuit38. The antenna matching circuit 38 is electrically connected at aground area thereof to a ground area of the first printed substrate 37a, and similarly, the high-frequency circuit 39 is also electricallyconnected at a grounded area thereof to a ground area of the firstprinted substrate 37 a.

[0086] In the cellular phone 30 in accordance with the secondembodiment, ground surfaces of the first and second printed substrates37 a and 37 b are used as an antenna ground.

[0087] The first high-frequency switch 40 includes a base contact 61, acontact plate 61 a designed pivotable around the base contact 61, afirst contact 62 and a second contact 63. The base contact 61 iselectrically connected to the control circuit 46. The first contact 62is electrically connected to a ground area of the first printedsubstrate 37 a. The second contact 63 is electrically connected at oneend to a ground area of the first printed substrate 37 a through theinductance coil 42.

[0088] The second high-frequency switch 41 includes a base contact 71, acontact plate 71 a designed pivotable around the base contact 71, afirst contact 72 and a second contact 73. The base contact 71 iselectrically connected to the control circuit 46. The first contact 72is electrically connected to a ground area of the second printedsubstrate 37 b. The second contact 73 is electrically connected at oneend to a ground area of the second printed substrate 37 b through theinductance coil 43.

[0089] Each of the inductance coils 42 and 43 is designed to have suchan inductance that they provide a sufficiently high impedance in ahigh-frequency band.

[0090] The base contacts 61 and 71 of the first and secondhigh-frequency switches 40 and 41 are electrically connected to eachother through a cable 47. A later mentioned control signal transmittedfrom the control circuit 46 is applied to the cable 10 and as a result,the first and second high-frequency switches 40 and 41 concurrentlyoperate, or make switching action in synchronization with each other.

[0091] For instance, the first and second high-frequency switches 40 and41 may be mounted in the hinge 33.

[0092] The detecting circuit 44 detects a frequency band in which thecellular phone 30 makes communication with others, and transmits adetection signal indicative of the thus detected frequency band, to thefrequency-band selecting circuit 45.

[0093] On receipt of the detection signal from the detecting circuit 44,the frequency-band selecting circuit 45 selects a desired frequencyband, and transmits a selection signal indicative of the thus selectedfrequency band, to the control circuit 46.

[0094] On receipt of the selection signal from the frequency-bandselecting circuit 45, the control circuit 46 transmits a control signalto both of the first and second high-frequency switches 40 and 41through the cable 47. In accordance with the control signal, the contactplates 61 a and 71 a make pivotal movement around the base contacts 61and 71 to thereby make electrical contact with the first contact 62, 72or the second contact 63, 73. The pivotal movement of the contact plates61 a and 71 a around the base contacts 61 and 71 between the first andsecond contacts 62, 72 and 63, 73 causes a ground length in the cellularphone 30 to vary in accordance with a frequency band.

[0095]FIG. 7 is a flow chart showing respective steps to be carried outin an operation of the cellular phone 30 in accordance with the secondembodiment. Hereinbelow is explained an operation of the cellular phone30 with reference to FIG. 7.

[0096] First, the detecting circuit 44 detects a frequency band in whichthe cellular phone 30 is making communication with another phone, instep S201. Then, the detecting circuit 44 transmits a detection signalindicative of the thus selected frequency band.

[0097] Then, the frequency-band selecting circuit 45 selects a desiredfrequency band in accordance with the frequency band indicated in thedetection signal received from the detecting circuit 44, in step S202.

[0098] Herein, it is assumed that the cellular phone 30 has to cover twofrequency bands, 800 MHz band and 2 GHz band.

[0099] For instance, if the frequency band detected by the detectingcircuit 44 or indicated in the detection signal is closer to 800 MHz,the frequency-band selecting circuit 45 selects 800 MHz, and transmits aselection signal indicative of 800 MHz.

[0100] Then, the frequency-band selecting circuit 45 transmits aselection signal indicative of the thus selected frequency band, to thecontrol circuit 46.

[0101] On receipt of the selection signal from the frequency-bandselecting circuit 45, the control circuit 46 transmits a control signalto the first and second high-frequency switches 40 and 41 through thecable 47, in step S203. The control signal includes indicationdetermined by the control circuit 46 in accordance with the selectionsignal transmitted from the frequency-band selecting circuit 45.

[0102] When the frequency-band selecting circuit 45 selects 800 MHz (YESin step S204), the contact plate 61 a is caused to make pivotal movementin a counter clock-wise direction to make electrical contact with thefirst contact 62, and the contact plate 71 a is caused to make pivotalmovement in a clock-wise direction to make electrical contact with thefirst contact 72, in step S205. Thus, the first body 31 of the cellularphone 30 is electrically connected directly to a ground area of thefirst printed substrate 37 a, and the second body 32 of the cellularphone 30 is electrically connected directly to a ground area of thesecond printed substrate 37 b.

[0103] As a result, the cellular phone 30 would have a ground lengthdefined as L2 illustrated in FIG. 6.

[0104] When the frequency-band selecting circuit 45 selects 2 GHz (No instep S204), the contact plate 61 a is caused to make pivotal movement ina clock-wise direction to make electrical contact with the secondcontact 63, and the contact plate 71 a is caused to make pivotalmovement in a counter clock-wise direction to make electrical contactwith the second contact 73, in step S206. Thus, the first body 31 of thecellular phone 30 is electrically connected to a ground area of thefirst printed substrate 37 a through the first inductance coil 42, andthe second body 32 of the cellular phone 30 is electrically connected toa ground area of the second printed substrate 37 b through the secondinductance coil 43. Since the first and second inductance coils 42 and43 have a sufficiently high impedance in a high frequency band, theground areas of the first and second printed substrates 37 a and 37 bare not electrically connected to each other in a high-frequency band.

[0105] As a result, the cellular phone 30 would have a ground lengthdefined as L1 smaller than the ground length L2.

[0106] The first and second high-frequency switches 40 and 41 may becomprised of a mechanical switch or an electrical switch. For instance,if each of the first and second high-frequency switches 40 and 41 iscomprised of an electrically controllable switch, the first and secondhigh-frequency switches 40 and 41 can be caused to automatically operateto thereby vary a ground length of the cellular phone 30, by detecting afrequency band of a radio signal received at the antenna 36.

[0107] Thus, it is possible in the cellular phone 30 to switch a lengthof a ground area with respect to the antenna matching circuit 38.

[0108] As mentioned above, in the foldable type cellular phone 30, sincea body is divided into two bodies (specifically, the first and secondbodies 37 a and 37 b) and a printed substrate is divided into twosubstrates (specifically, the first and second printed substrates 37 aand 37 b) both about the hinge 33. Hence, it is possible in the foldabletype cellular phone 30 to electrically connect the two bodies or groundareas of the two substrates to each other or not to electrically connectthem to each other by making use of the hinge 33. As a result, it ispossible to vary a ground length defined with the antenna 36 beingconsidered as a reference point, and hence, accomplish an optimal groundlength for each of frequency bands, ensuring desired characteristics ofthe antenna 36 which can prevent generation of null points.

[0109] Though the cellular phone 30 in accordance with the secondembodiment is designed to have the circuitry illustrated in FIG. 6, thecellular phone 30 may be designed to have the circuitry illustrated inFIG. 2. Similarly, the cellular phone 10 in accordance with the firstembodiment may be designed to have the circuitry illustrated in FIG. 6in place of the circuitry illustrated in FIG. 2.

[0110] The cellular phone 30 in accordance with the second embodimentmay be designed to include a circuit for detecting whether the first andsecond bodies 31 and 32 are open or closed to each other, in place ofthe detecting circuit 44. In the case, the frequency-band selectingcircuit 45 is designed to select a desired frequency band in accordancewith a signal transmitted from the circuit which signal is indicative ofwhether the first and second bodies 31 and 32 are open or closed to eachother.

[0111] [Third Embodiment]

[0112]FIGS. 8A and 8B are perspective views of a cellular phone 50 inaccordance with the third embodiment.

[0113] The cellular phone 50 is of a slide type.

[0114] The cellular phone 50 is comprised of a principal body 51 and aslide body 52 designed slidable relative to the principal body 51.

[0115] The principal body 51 includes an antenna 53, a liquid crystaldisplay 54, and a plurality of keys 55 some of which appear only whenthe slide body 52 is slid relative to the principal body 51 in adirection R. The slide body 52 has a microphone 56.

[0116] The slide body 52 is formed hollow, and thus, the principal body51 can be inserted partially into the slide body 52, as illustrated inFIG. 8A. In addition, the slide body 52 is designed slidable relative tothe principal body 51, as illustrated in FIG. 8B. Specifically, theslide body 52 can have a first position in which the principal body 51is inserted into the slide body 52, and hence, the cellular phone 50 hasa longitudinal length of La, and a second position in which the slidebody 52 is slid relative to the principal body 51 in the direction R,and hence, the cellular phone 50 has a longitudinal length Lb longerthan the length La.

[0117] The cellular phone 50 may be designed to have the same internalcircuitry as that of the cellular phone 30 illustrated in FIG. 6. Whenthe slide body 52 is in the first position illustrated in FIG. 8A, thecellular phone 50 has a ground length of L1, whereas when the slide body52 is in the second position illustrated in FIG. 8B, the cellular phone50 has a ground length of L2 longer than the ground length LI.

[0118] As is obvious in view of the explanation made above, even if thecellular phone 50 is designed to be of a slide type, it can have thesame functions as those of the cellular phone 30 which is of a foldabletype.

[0119] An operation of the frequency-band selecting circuit 19 and thecontrol circuit 20 in the cellular phone 10, and the detecting circuit44, the frequency-band selecting circuit 45 and the control circuit 46in the cellular phone 30 can be accomplished by a computer programwritten in a language readable by a computer.

[0120] For operating the frequency-band selecting circuit 19 and thecontrol circuit 20 in the cellular phone 10, and the detecting circuit44, the frequency-band selecting circuit 45 and the control circuit 46in the cellular phone 30 by means of a computer program, the cellularphones 10 and 30 are designed to include a memory to store a computerprogram therein, and a central processing unit, for instance. Thecomputer program is stored in the memory, and is read out into thecentral processing unit when the central processing unit starts itsoperation. Thus, such an operation of the cellular phones 10 and 30 asmentioned above is accomplished in accordance with the computer program.

[0121] As an alternative, a recording medium storing such a computerprogram as mentioned above may be set into the central processing unitto be read out by the central processing unit.

[0122] The functions accomplished by a computer program are defined byvarious commands, and may be presented through a recording mediumreadable by a computer.

[0123] In the specification, the term “recording medium” means anymedium which can record data therein.

[0124] The term “recording medium” includes, for instance, a disk-shapedrecorder such as CD-ROM (Compact Disk-ROM) or PD, a magnetic tape, MO(Magneto Optical Disk), DVD-ROM (Digital Video Disk-Read. Only Memory),DVD-RAM (Digital Video Disk-Random Access Memory), a floppy disk, amemory chip 404 such as RAM (Random Access Memory) or ROM (Read OnlyMemory), EPROM (Erasable Programmable Read Only Memory), EEPROM(Electrically Erasable Programmable Read Only Memory), smart media(Registered Trade Mark), a flush memory, a rewritable card-type ROM suchas a compact flush card, a hard disk 403, and any other suitable meansfor storing a program therein.

[0125] A recording medium storing a program for accomplishing theabove-mentioned apparatus may be accomplished by programming functionsof the above-mentioned apparatuses with a programming language readableby a computer, and recording the program in a recording medium such asmentioned above.

[0126] A hard disc equipped in a server may be employed as a recordingmedium. It is also possible to accomplish the recording medium inaccordance with the present invention by storing the above-mentionedcomputer program in such a recording medium as mentioned above, andreading the computer program by other computers through a network.

[0127] The advantages obtained by the aforementioned present inventionwill be described hereinbelow.

[0128] In accordance with the present invention, a ground length for anantenna matching circuit is varied to thereby prevent generation of nullpoints in an antenna irradiation pattern in a plurality of frequencybands different from each other. In particular, a foldable type cellularphone such as the cellular phone 30 in accordance with the secondembodiment can switch a ground length by detecting whether first andsecond bodies thereof are open or closed to each other.

[0129]FIGS. 9A and 9B illustrate the results of antenna irradiationpattern simulation having been carried out using a λ/4 element, whereinground lengths were 170 mm and 50 mm, and a frequency band was 880 MHz.

[0130]FIGS. 10A and 10B illustrate the results of antenna irradiationpattern simulation having been carried out using a λ/4 element, whereinground lengths were 170 mm and 50 mm, and a frequency band was 2 GHz.

[0131]FIGS. 11A and 11B illustrate the results of antenna irradiationpattern simulation having been carried out using a λ/4 element, whereinground lengths were 50 mm and 50 mm, and a frequency band was 2 GHz.

[0132] Comparing the results of FIGS. 9A and 9B to the results of FIGS.10A and 10B in both of which the ground lengths are set equal to eachother, the greater number of null points can be seen in FIGS. 10A and10B than in FIGS. 9A and 9B, that is, the greater number of null pointsgenerate in a higher frequency band.

[0133] Comparing the results of FIGS. 10A and 10B to the results ofFIGS. 11A and 11B in both of which the frequency band is set equal toeach other, the greater number of null points can be seen in FIGS. 10Aand 10B than in FIGS. 11A and 11B, that is, the greater number of nullpoints generate in a longer ground length. In FIGS. 11A and 11B whereinthe ground length is set shorter than the same in the simulationillustrated in FIGS. 10A and 10B, no null points can be seen.

[0134] As will be obvious in view of the comparison among FIGS. 9A to11B, the present invention makes it possible to prevent generation ofnull points by selecting a higher frequency band and/or selecting ashorter ground length.

[0135] While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

[0136] The entire disclosure of Japanese Patent Application No.2002-139141 filed on May 14, 2002 including specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A cellular phone covering a plurality offrequency bands, comprising: (a) an antenna; (b) a high-frequencycircuit; (c) an antenna-matching circuit electrically connecting inseries between said antenna and said high-frequency circuit; and (d) afirst unit which varies a ground length in accordance with a frequencyband in which said cellular phone makes communication with others, saidground length being defined as a length of a ground area for saidantenna-matching circuit.
 2. The cellular phone as set forth in claim 1,wherein said first unit is comprised of: (d1) a detector which detects afrequency band in which said cellular phone makes communication withothers, and transmits a detection signal indicative of the thus detectedfrequency band; and (d2) a second unit which receives said detectionsignal, and varies said ground length in accordance with a frequencyband indicated in the detection signal.
 3. The cellular phone as setforth in claim 2, further comprising a first printed substrate, andwherein said second unit is comprised of a first switch formed on saidfirst printed substrate, wherein said first switch is grounded when saiddetection signal indicates a first frequency band, and makes animpedance circuit when said detection signal indicates a secondfrequency band greater than said first frequency band.
 4. The cellularphone as set forth in claim 3, wherein said second unit further includesa first inductance, and wherein said first switch is electricallyconnected to said first inductance to thereby make said impedancecircuit when said detection signal indicates said second frequency band.5. The cellular phone as set forth in claim 3, wherein said first switchis comprised of an electrically controllable switch which isautomatically grounded or automatically makes said impedance circuit inaccordance with a frequency band indicated in said detection signal. 6.The cellular phone as set forth in claim 2, further comprising first toN-th printed substrates wherein N is a positive integer equal to orgreater than two, wherein said second unit is comprised of first to N-thswitches formed on said first to N-th printed substrates, respectively,said first to N-th switches operate in synchronization with one another,said first to N-th switches are grounded when said detection signalindicates a first frequency band, and make an impedance circuit whensaid detection signal indicates a second frequency band greater thansaid first frequency band.
 7. The cellular phone as set forth in claim6, wherein said second unit further includes first to N-th inductances,and wherein said first to N-th switches are electrically connected tosaid first to N-th inductances, respectively, to thereby make saidimpedance circuit when said detection signal indicates said secondfrequency band.
 8. The cellular phone as set forth in claim 6, whereineach of said first to N-th switches is comprised of an electricallycontrollable switch which is automatically grounded or automaticallymakes said impedance circuit in accordance with a frequency bandindicated in said detection signal.
 9. The cellular phone as set forthin claim 6, wherein said first to N-th switches are electricallyconnected to one another through a cable to which said detection signalis transmitted such that said first to N-th switches operate insynchronization with one another.
 10. The cellular phone as set forth inclaim 1, wherein said cellular phone is of a straight type or a slidetype.
 11. The cellular phone as set forth in claim 2, wherein saidcellular phone is comprised of a first body, and a second bodymechanically connected to said first body through a hinge such that saidsecond body is rotatable at an end thereof relative to said first body,said cellular phone further includes a first printed substrate arrangedin said first body, and a second printed substrate arranged in saidsecond body, said second unit further includes a first switch formed onsaid first printed substrate, and a second switch formed on said secondprinted substrate and is driven in synchronization with said firstswitch, and said first and second switches are grounded when saiddetection signal indicates a first frequency band, and make an impedancecircuit when said detection signal indicates a second frequency bandgreater than said first frequency band.
 12. The cellular phone as setforth in claim 11, wherein said second unit further includes first andsecond inductances, and wherein said first and second switches areelectrically connected to said first and second inductances,respectively, to thereby make said impedance circuit when said detectionsignal indicates said second frequency band.
 13. The cellular phone asset forth in claim 11, wherein each of said first and second switches iscomprised of an electrically controllable switch which is automaticallygrounded or automatically makes said impedance circuit in accordancewith a frequency band indicated in said detection signal.
 14. Thecellular phone as set forth in claim 11, wherein said first and secondswitches are electrically connected to each other through a cable towhich said detection signal is transmitted such that said first andsecond switches operate in synchronization with each other.
 15. Thecellular phone as set forth in claim 1, wherein said cellular phone iscomprised of a first body, and a second body mechanically connected tosaid first body through a hinge such that said second body is rotatableat an end thereof relative to said first body, said first unit iscomprised of: (d1) a detector which detects whether said first andsecond bodies are open or closed to each other, and transmits a seconddetection signal indicative of the detection of said second detector;and (d2) a second unit which receives said detection signal, and variessaid ground length in accordance with the detection of said seconddetector.
 16. The cellular phone as set forth in claim 15, wherein saidsecond unit further includes first and second inductances, and whereinsaid first and second switches are electrically connected to said firstand second inductances, respectively, to thereby make said impedancecircuit when said detection signal indicates said second frequency band.17. The cellular phone as set forth in claim 15, wherein each of saidfirst and second switches is comprised of an electrically controllableswitch which is automatically grounded or automatically makes saidimpedance circuit in accordance with a frequency band indicated in saiddetection signal.
 18. The cellular phone as set forth in claim 15,wherein said first and second switches are electrically connected toeach other through a cable to which said detection signal is transmittedsuch that said first and second switches operate in synchronization witheach other.
 19. A method of operating a cellular phone covering aplurality of frequency bands, including the steps of: (a) detecting afrequency band in which said cellular phone makes communication withothers; and (b) varying a ground length in accordance with saidfrequency band detected in said step (a), said ground length beingdefined as a length of a ground area for an antenna-matching circuit ofsaid cellular phone.
 20. The method as set forth in claim 19, whereinsaid cellular phone includes a first printed substrate, and a firstswitch formed on said first printed substrate, said method furthercomprising the step of grounding said first switch when said cellularphone makes communication in a first frequency band, and causing saidfirst switch to make an impedance circuit when said cellular phone makescommunication in a second frequency band greater than said firstfrequency band.
 21. The method as set forth in claim 20, wherein saidcellular phone further includes a first inductance, said method furtherincluding the step of electrically connecting said first switch to saidfirst inductance to thereby make said impedance circuit.
 22. The methodas set forth in claim 19, wherein said cellular phone further includesfirst to N-th printed substrates wherein N is a positive integer equalto or greater than two, and first to N-th switches formed on said firstto N-th printed substrates, respectively, and said first to N-thswitches operate in synchronization with one another, said methodfurther including the step of grounding said first to N-th switches whensaid cellular phone makes communication in a first frequency band, andcausing said first to N-th switches to make an impedance circuit whensaid cellular phone makes communication in a second frequency bandgreater than said first frequency band.
 23. The method as set forth inclaim 22, wherein said cellular phone further includes first to N-thinductances, said method further including the step of electricallyconnecting said first to N-th switches to said first to N-thinductances, respectively, to thereby make said impedance circuit.
 24. Amethod of operating a cellular phone covering a plurality of frequencybands, said cellular phone being comprised of a first body, and a secondbody mechanically connected to said first body through a hinge such thatsaid second body is rotatable at an end thereof relative to said firstbody, said method including the steps of: (a) detecting whether saidfirst and second bodies are open or closed to each other; and (b)varying a ground length in accordance with the result of said step (a),said ground length being defined as a length of a ground area for anantenna-matching circuit of said cellular phone.
 25. The method as setforth in claim 24, wherein said cellular phone includes a first printedsubstrate arranged in said first body, a first switch formed on saidfirst printed substrate, a second printed substrate arranged in saidsecond body, and a second switch formed on said second printedsubstrate, said method further comprising the step of grounding saidfirst and second switches when said cellular phone makes communicationin a first frequency band, and causing said first and second switches tomake an impedance circuit when said cellular phone makes communicationin a second frequency band greater than said first frequency band. 26.The method as set forth in claim 24, wherein said cellular phone furtherincludes first and second inductances, said method further including thestep of electrically connecting said first and second switches to saidfirst and second inductances, respectively, to thereby make saidimpedance circuit.
 27. A program for causing a computer to carry out amethod of operating a cellular phone covering a plurality of frequencybands, processing executed by said computer in accordance with saidprogram including: (a) detecting a frequency band in which said cellularphone makes communication with others; and (b) varying a ground lengthin accordance with said frequency band detected in said processing (a),said ground length being defined as a length of a ground area for anantenna-matching circuit of said cellular phone.
 28. A program forcausing a computer to carry out a method of operating a cellular phonecovering a plurality of frequency bands, said cellular phone beingcomprised of a first body, and a second body mechanically connected tosaid first body through a hinge such that said second body is rotatableat an end thereof relative to said first body, processing executed bysaid computer in accordance with said program including: (a) detectingwhether said first and second bodies are open or closed to each other;and (b) varying a ground length in accordance with the result of saidstep (a), said ground length being defined as a length of a ground areafor an antenna-matching circuit of said cellular phone.